USPTO Patents Application 10500820

DESCRIPTION

UNIT-TO-UNIT DATA EXCHANGE SYSTEM, AND UNIT, EXCHANGE COMPLETION
DATA KEEPING DEVICE AND PROGRAM FOR USE IN THE SAME

5

TECHNICAL FIELD BACKGROUND OF THE INVENTION
1. Field of the Invention

The present invention relates to a system for exchanging
electronic data between units, and more particularly to a system
10 in which the exchange process can be completed in a fair manner
for both of the units involved in the exchange process.

BACKGROUND ART

2. Description of the Related Art
15 With high-speed communications networks, such as ADSL

(Asymmetric Digital Subscriber Line) and FTTH (Fiber To The Home) ,
becoming more widespread in recent years, P2P (Peer To Peer) data
exchange systems have been used for exchanging electronic data
between units.

20 Early P2P systems were pure P2P data exchange systems in

which each system included only two units. For example, WinMX
is one of such systems. In a pure P2P data exchange system, a
unit only has 1) a function of requesting the other party's unit
to transmit data of interest, 2) a function of transmitting data

25 requested by the other party's unit, 3) a function of receiving

data from the other party f s unit , and 4) a function of discontinuing
data transmission to the other party f s unit . With these functions ,
data can be transmitted and received by each other. However, due
to the difference in data size between exchanged data or the
5 difference in data transmission/reception speedbetween the units,
one unit may complete receiving data earlier than the other unit.
Therefore, in a pure P2P data exchange system, a first party may
discontinue the data transmission to a second party when the first
party completes receiving the data of interest—, thus This unfairly
10 preventing prevents the second party from completing the data
reception while the first party has completed receiving the data
of interest.

In view of this, methods for preventing such an unfair
practice have been proposed in the art, in which a server is provided
15 that functions as a mediator for the data exchange process (see,
for example, United States Patent No. 6061792, and "Asynchronous
Protocols for Optimistic Fair Exchange" by N . Asokan, Victor Shoup
andMichael Waidner, Research Report RZ 2 97 6 (#93022), IBMResearch,
December 1997) .

20 In such a P2P data exchange system with a mediator server,

data to be exchanged arc is first uploaded to the mediator server
before initiating the data exchange between the units so that it
is possible to address a situation where either unit fails to obtain
the data of interest due to a certain problem during the data exchange

25 between the units . In the P2P data exchange system with a mediator

server, even if one terminal becomes unable to obtain the data
of interest during the data exchange between the units, the unit
failing to obtain the data of interest can be complemented with
the data from the mediator server because the mediator server has
5 the data being exchanged.

DISCLOSURE BRIEF DESCRIPTION OF THE INVENTION
The following problems arise when using a pure P2P data
exchange system such as WinMx . If an unfair practice^ as described

10 above^ occurs during a data exchange between units, the user of
one unit may wish to discontinue the data exchange. For example,
in a data exchange between unit A and unit B, if unit A obtains
data of interest earlier than unit A — B and terminates the
communication session with unit B, the user of unit B may be

15 displeased by the failure to obtain data from unit A and may desire
to stop the data exchange with unit A. However, in such a situation,
unit B is no longer able to, for example, invalidate or retrieve
the data that has been completely passed to unit A. Thus, in a
conventional pure P2P data exchange system, a unit cannot cancel

20 a data exchange that is once decided to be performed if the other
unit first completes receiving data of interest. Therefore, in
the case of an unfair exchange, there may occur a situation where
only one party gains to obtain the data of interest while the other
party gains nothing.

25 In a P2P data exchange system with a mediator server, data

arc is exchanged between terminals after the data are is once
uploaded to the mediator server. Therefore, if the communication
session fails for one terminal, data is transmitted to the terminal
from the mediator server, thereby ensuring that both terminals
obtain data of interest. However, since data to be exchanged
between the units need to be first uploaded to the mediator server,
the communications cost and the load on the mediator server increase
in proportion to the amount of the exchanged data.

Therefore, an object of the present invention is to provide
(i) a unit-to-unit data exchange system in which an unfair exchange
is prevented without increasing the communications cost or the
load on the server, and (ii) a unit, and (iii) a server and a program
for use in such a system. To achieve the above object, the present
invention has the following aspects . A first aspect of the present
invention is directed to a system for exchanging data between units
connected to each other via a communications medium-^ including :
This system includes: a first unit having at least one piece of
data that can be exchanged and requesting to exchange data with
another unit; a second unit having data of interest to the first
unit; and an exchange completion data keeping device connected
to the first and second units via the communications mediu m, the
exchange completion data keeping device being (i) for keeping
first exchange completion data that is necessary, after completion
of the data exchange between the first and second units, (ii) for
reproducing data obtained by the first unit and second exchange

completion data that is necessary, after completion of the data
exchange between the first and second units, and (iii) for
reproducing data obtained by the second unit, wherein the exchange
completion data keeping device includes exchange completion data
5 transmission means for transmitting the first exchange completion
data to the first unit and the second exchange completion data
to the second unit only when the first and second units have
successfully received data of interest.

Preferably, the first unit includes: first exchange

10 completion data production means for producing the second exchange
completion data; and first exchange completion data transmission
means for transmitting the second exchange completion data produced
by the first exchange completion data production means to the
exchange completion data keeping device ^. Further, the second unit

15 includes: second exchange completion data production means for
producing the first exchange completion data; and second exchange
completion data transmission means for transmitting the first
exchange completion data produced by the second exchange completion
data production means to the exchange completion data keeping

20 device^ and — trhe — The exchange completion data keeping device
further includes exchange completion data keepingmeans for keeping
the first and second exchange completion data transmitted from
the exchange completion data transmission means so that each unit
from which the exchange completion data has been transmitted can

25 be identified.

Preferably, the first unit further includes: first data
conversion means for converting data owned by the first unit to
data that can be reproduced successfully only by using the second
exchange completion data; and first data recovery means for
5 recovering data that can be reproduced successfully from data
received from the second unit by using the first exchange completion
datat. and Further, the second unit further includes: second data
conversion means for converting data owned by the second unit to
data that can be reproduced successfully only by using the first
10 exchange completion data; and second data recovery means for
recovering data that can be reproduced successfully from data
received from the first unit by using the second exchange completion
data .

Preferably, the first unit further includes first exchange
15 completion data production requesting means for requesting the
exchange completion data keeping device to produce the second
exchange completion datat^ In addition, the second unit further
includes second exchange completion data production requesting
means for requesting the exchange completion data keeping device
20 to produce the first exchange completion data^. and the The exchange
completion data keeping device further includes: exchange
completion data production means for producing the first and second
exchange completion data in response to the requests from the first
and second exchange completion data production requesting means;
25 and exchange completion data keeping means for keeping the first

and second exchange completion data produced by the exchange
completion data production means so that each requesting unit can
be identified.

Preferably, each of the first and second units further
includes: data conversion means for converting first data owned
by the unit to second data that can be reproduced successfully
only by using the exchange completion data; and data recovery means
for recovering data that can be reproduced successfully from data
received from the other unit by using the exchange completion data
transmitted from the exchange completion data transmission meanst^
the The exchange completion data keeping device further includes
conversion process data production/transmission means for
producing first and second conversion process data used for ( i )
converting the first data to the second data that can be reproduced
successfully by using the first and second exchange completion
data, and (ii) transmitting the first conversion process data to
the second unit and the second conversion process data to the first
unit^ the The data conversion means of the first unit converts
the first data to the second data by using the second conversion
process data from the conversion process data transmission meanst^
and the The data conversion means of the second unit converts
the first data to the second data by using the first conversion
process data from the conversion process data transmission means.

For example, the first conversion process data is a first
encryption key^ the first exchange completion data is a first

decryption key corresponding to the first encryption key^ the
second conversion process data is a second encryption keyt^ and
the second exchange completion data is a second decryption key
corresponding to the second encryption key.

Preferably, each of the first and second units further
includes communication result notification means for notifying
the exchange completion data keeping device of a communication
result when a communication session with the other unit is

terminated ^and Further, the exchange completion data

transmission means determines whether or not both of the first
and second units have successfully received data of interest based
on the communication results from the communication result
notification means of the first unit and that of the second unit.

Preferably, the communication result is information
indicating whether or not the data of interest has been received
successfully^, and the The exchange completion data transmission
means transmits exchange completion data if the exchange completion
data transmission means receives information indicating that the
data has been received successfully from both the first and second
units .

For example, the first exchange completion data is a
decryption key used for decrypting data given by the second unit
to the first unitt^ and the second exchange completion data is
a decryption key used for decrypting data given by the first unit
to the second unit.

8

Preferably, each of the first and second units further
includes resend requesting means for requesting the other unit
to resend data of interest if the unit fails to fully receive the
data of interest.
5 A second aspect of the present invention is directed to a

unit for exchanging data owned by the unit with data of interest
owned by another unit- j_ including: The unit includes: exchange
completion data production means for producing first exchange
completion data that is necessary for reproducing the data owned

10 by the unit; exchange completion data registration means for
registering the first exchange completion data produced by the
exchange completion data product ion means at an exchange completion
data keeping device for keeping exchange completion data; and
exchange completion data obtaining means for obtaining, from the

15 exchange completion data keeping device, second exchange
completion data that is necessary for reproducing data obtained
from the other unit when a communication session with the other
unit is terminated.

Preferably, the unit further includes : data conversion means

20 for converting data owned by the unit to data that can be reproduced
successfully only by using the first exchange completion data;
and data recovery means for recovering data that can be reproduced
successfully from data received from the other unit by using the
second exchange completion data obtained by the exchange completion

25 data obtaining means.

Preferably, the unit further includes exchange history
storing means for storing a history of data exchanges made with
other units, wherein: the data conversion means changes a data
conversion method based on the exchange history; and the exchange
5 completion data production means changes a method of producing
exchange completion data based on the exchange history.

Preferably, the unit further includes resend requesting
means for requesting the other unit to resend data of interest
if the unit fails to fully receive the data of interest.

10 A third aspect of the present invention is directed to a

unit for exchanging data owned by the unit with data of interest
owned by another unit— j_ including ; — The unit includes: exchange
completion data production requesting means for requesting an
exchange completion data keeping device for keeping exchange

15 completion data to produce first exchange completion data that
is necessary for reproducing the data owned by the unit; and exchange
completion data obtaining means for obtaining, from the exchange
completion data keeping device, second exchange completion data
that is necessary for reproducing data obtained from the other

20 unit when a communication session with the other unit is terminated.

Preferably, the unit further includes: conversion process
data reception means for receiving conversion process data used
for converting the data owned by the unit so that the data can
be reproduced successfully by using the first exchange completion

25 data sent from the exchange completion data keeping device; data

conversion means for converting the data owned by the unit by using
the conversion process data received by the conversion process
data reception means; and data recovery means for recovering data
that can be reproduced successfully from data obtained from the
5 other unit by using the second exchange completion data obtained
by the exchange completion data obtaining means.

Preferably, the unit further includes: exchange history
storing means for storing a history of data exchanges made with
other units ; and conversion method notification means for notifying

10 the exchange completion data keeping device of a conversion method
used by the data conversion means based on the exchange history,
wherein the data conversion means converts the data owned by the
unit by using conversion process data using the specified
conversion method sent from the exchange completion data keeping

15 device.

Preferably, the unit further includes resend requesting
means for requesting the other unit to resend data of interest
if the unit fails to fully receive the data of interest.

A fourth aspect of the present invention is directed to an

20 exchange completion data keeping device used in a system for
exchanging data between units connected to each other via a
communications medium—^ including: The exchange completion data
keeping device includes: exchange completion data keeping means
for keeping exchange completion data necessary for reproducing

25 data exchanged between a first unit and a second unit; and exchange

11

completion data transmission means for transmitting exchange
completion data that is necessary for reproducing data obtained
by the first unit to the first unit and transmitting exchange
completion data that is necessary for reproducing data obtained
5 by the second unit to the second unit only when both of the first
and second units have successfully received data of interest.

Preferably, the exchange completion data keeping device
further includes: exchange completion data production means for
producing the exchange completion data in response to a request

10 from the first and second units; and exchange completion data
keeping means for keeping the exchange completion data produced
by the exchange completion data production means so that each
requesting unit can be identified.

Preferably, the exchange completion data keeping device

15 further includes conversion process data production/transmission
means for producing conversion process data such that exchanged
data can be reproduced successfully at the first and second units
by using the exchange completion data produced by the exchange
completion data production means, and for transmitting the

20 conversion process data to the first and second units.

Preferably, the exchange completion data transmission means
determines whether or not both of the first and second units have
successfully received data of interest based on communication
results from the first and second units.

25 For example, the communication result is information

12

indicating whether or not the data of interest has been received
successfullyt. and the The exchange completion data transmission
means transmits exchange completion data when receiving
information indicating that the data has been received successfully
5 from the first and second units.

Preferably, the exchange completion data keeping device
further includes exchange completion data deletion means for
deleting exchange completion data kept by the exchange completion
data keeping device if a predetermined condition is met.

10 For example, the predetermined condition is such that the

exchange completion data deletion means deletes exchange
completion data transmitted to the first and second units from
the exchange completion data transmission means if the first and
second units have successfully received the transmitted exchange

15 completion data.

For example, the predetermined condition is such that the
exchange completion data deletion means deletes the exchange
completion data registered by the first and second units if the
exchange completion data deletion means is notified from either

20 unit that the data of interest has not been received successfully.

A fifth aspect of the present invention is directed to a
program for instructing a computer device to exchange data owned
by the computer device with data of interest owned by another
computer device—, including the steps of: The program causing the

25 computer device to execute a method including: instructing the

13

computer device to produce first exchange completion data that
is necessary for reproducing the data owned by the computer device;
instructing the computer device to register the produced first
exchange completion data at an exchange completion data keeping
5 device for keeping exchange completion data; and instructing the
computer device to obtain, from the exchange completion data
keeping device, second exchange completion data that is necessary
for reproducing data obtained from the other computer device when
a communication session with the other computer device is

10 terminated.

A sixth aspect of the present invention is directed to a
program for instructing a computer device to exchange data owned
by the computer device with data of interest owned by another
computer device—. including the steps of: — The program causing

15 the computer device to execute a method including: instructing
the computer device to request an exchange completion data keeping
device for keeping exchange completion data to produce first
exchange completion data that is necessary for reproducing the
data owned by the computer device; and instructing the computer

20 device to obtain, from the exchange completion data keeping device,
second exchange completion data that is necessary for reproducing
data obtained from the other computer device when a communication
session with the other computer device is terminated.

A seventh aspect of the present invention is directed to

25 a program for instructing a computer device, which is used in a

14

system for exchanging data between computer devices connected to
each other via a communications medium, to function as: exchange
completion data keeping means for keeping exchange completion data
necessary for reproducing data exchanged between a first computer
5 device and a second computer device; and exchange completion data
transmission means for transmitting exchange completion data that
is necessary for reproducing data obtained by the first computer
device to the first computer device and for transmitting exchange
completion data that is necessary for reproducing data obtained

10 by the second computer device to the second computer device only
when both of the first and second computer devices have successfully
received data of interest.

The effects of the present invention will now be described.
According to the present invention, the data to be exchangedbetween

15 units will not themselves be uploaded to the mediating server (the
exchange completion data keeping device) , but only those data (the
exchange completion data) that are necessary for completing the
data exchange are uploaded to the exchange completion data keeping
device being the server. This reduces the problem that the

20 communications cost and the load on the mediator server increase
in proportion to the amount of data exchanged between units. In
addition, according to the present invent ion, two units exchanging
data with each other can obtain the exchange completion data only
when both of the units have successfully received data of interest .

25 Therefore, in the case of an abnormal termination of the

communication session, e.g., in the case of disconnection on the
side of one unit whereby the other unit fail to successfully receive
the data of interest, one of the units that has terminated the
communication session cannot obtain the exchange completion data.
5 Then, neither of the units will be able to reproduce the data of
interest. Thus, a fair data exchange system is realized.

Moreover, the exchange completion data is produced by each
unit, thereby further reducing the load on the mediating server.
Each unit transmits its data to the other party's unit after

10 converting it to data that cannot be reproduced successfully
without the use of exchange completion data. Therefore, the other
party's unit cannot successfully reproduce the data unless it
obtains the exchange completion data.

Conversely, the server may produce the exchange completion

15 data, in which case each unit does not have to include means for
producing the exchange completion data, thus reducing the load
on the unit.

For example, a unit may encrypt data and transmit the
encrypted data to the other party's unit, and received data can
20 be reproduced by using a decryption key as encrypted exchange
completion data . Then, it is possible to easily realize the system
of the present invention by employing commonly-available
encryption/ decryption software .

The exchange completion data keeping device determines
25 whether or not each unit exchanging its data with another has

successfully received data based on the communication result sent
from the unit. Therefore, it is possible to easily determine
whether or not the data exchange has been performed successfully.

If a unit fails to completely receive data of interest, the
5 unit issues a resend request to the other party's unit, ensuring
that the unit can completely receive the data of interest.

A unit may produce the exchange completion data based on
its history of data exchanges made with other units to simplify
the recovery process at the other party's unit. Thus, it is

10 possible to provide an easy-to-use system in which an exchange
with a highly trusted party can be performed quickly. Moreover,
a unit may simplify the conversion of data to be transmitted based
on its history of data exchanges made with other units, whereby
a data exchange with a highly trusted party can be performed more

15 quickly.

If a predetermined condition is met, the exchange completion
data is deleted from the network, whereby it is possible to prevent
the exchange completion data from being left unremoved for a long
time and being misused.
20 The program of the present invention can be distributed to

each party 1 s computer device to realize an easy-to-use unit-to-unit
data exchange system, thus facilitating the circulation of
information contents .

25 BRIEF DESCRIPTION OF THE DRAWINGS

17

FIG. 1 is a block diagram illustrating a general
configuration of a unit-to-unit data exchange system Sa with a
mediator server according to a first embodiment of the present
invention .

5 FIG. 2 is a block diagram illustrating a functional

configuration of the inside of a unit 11.

FIG. 3 is a diagram illustrating an exemplary data structure
of data including data IDs and associated public data IDs.

FIG. 4 is a diagram illustrating an exemplary data structure
10 of data associated with the data IDs of FIG. 3.

FIG. 5 is a diagram illustrating a data structure of public
contents information associated with the public data IDs of FIG.
3.

FIG. 6 is a block diagram illustrating a detailed functional
15 configuration of the inside of a data conversion section 111.

FIG. 7 is a block diagram illustrating a functional
configuration of the inside of an exchange completion data keeping
device 21 .

FIG. 8 is a diagram illustrating an exemplary data structure
20 of a determination table.

FIG. 9 is a diagram illustrating an exemplary data structure
of exchange completion data associated with exchange completion
data IDs of FIG. 8.

FIG. 10 is ablock diagram illustrating a detailed functional
25 configuration of the inside of an exchange completion data

transmission determination section 211.

FIG. 11 is a block diagram illustrating a functional
configuration of the inside of a public data keeping device 31.

FIG. 12 is a diagram illustrating an exemplary data structure
5 of public data list.

FIG. 13 is a diagram illustrating an exemplary data structure
of contents information associated with public data IDs of FIG.
12 .

FIG. 14 is a sequence diagram illustrating an operation of
10 the unit 11 and the public data keeping device 31 when the unit
11 registers the contents information on its public data at the
public data keeping device 31.

FIG. 15 is a sequence diagram illustrating an operation of
the public data keeping device 31 and the unit 11 when the public
15 data keeping device 31 receives a REGI STER_PUBLIC_DATA message.

FIG. 16 is a sequence diagram illustrating an operation of
a unit 11a when obtaining a unit ID.

FIG. 17 is a sequence diagram illustrating an operation of
the public data keeping device 31 and the unit 11a when the public
20 data keeping device 31 receives an OBTAIN_REGISTERING_UNIT_ID
message .

FIG. 18 is a sequence diagram illustrating an operation of
the unit 11a and a unit lib from when the unit 11a requests the
unit lib to exchange data until the unit 11a receives a response
25 thereto.

19

FIG. 19 is a sequence diagram illustrating an operation of
the unit 11a and the exchange completion data keeping device 21
from when the unit 11a requests the exchange completion data keeping
device 21 for mediation until the unit 11a receives a response
5 thereto in a case where an ACK message received from the unit lib
includes a public data ID of data requested by the unit 11a.

FIG. 20 is a sequence diagram illustrating an operation of
the unit 11a and the unit lib from when the unit 11a receives an
ACK message from the exchange completion data keeping device 21
10 until the unit 11a starts a data exchange with the unit lib.

FIG. 21 is a sequence diagram illustrating an operation of
the unit 11a and the exchange completion data keeping device 21
from when the unit 11a terminates the communication session with
the unit lib until the unit 11a receives an ACK message from the
15 exchange completion data keeping device 21.

FIG. 22 is a sequence diagram illustrating an operation of
the unit 11a after receiving an ACK message from the exchange
completion data keeping device 21.

FIG. 23 is a sequence diagram illustrating an operation of
20 the unit lib when the unit lib receives an EXCHANGE_DATA message
from the unit 11a.

FIG. 24 is a sequence diagram illustrating an operation of
the exchange completion data keeping device 21 when the exchange
completion data keeping device 21 receives a
25 REGISTER_EXCHANGE_COMPLETION_DATA message from the unit 11a and

from the unit lib.

FIG. 25 is a sequence diagram illustrating an operation of
the unit lib when the unit lib receives an INITIATE_EXCHANGE message
from the unit 11a.
5 FIG. 26 is a sequence diagram illustrating an operation of

the exchange completion data keeping device 21 when the exchange
completion data keeping device 21 receives an EXCHANGE_COMPLETED
message from the unit 11a and from the unit lib.

FIG. 27 is a flow chart illustrating an operation of the
10 exchange completion data keeping device 21 until exchange
completion data is deleted.

FIG. 28 is a sequence diagram illustrating an operation of
the unit 11a and the unit lib when the unit 11a requests the unit
lib to resend data to be exchanged.
15 FIG. 29 is a diagram illustrating an exemplary data structure

of an exchange history stored in the unit 11.

FIG. 30 is a flow chart illustrating an operation of the
unit 11a when requesting the unit lib to exchange data.

FIG. 31 is a flow chart illustrating an operation of the
20 unit 11a when producing exchange completion data at an exchange
completion data keeping device.

BEST MODE FOR CARRYING OUT DETAILED DESCRIPTION OF THE INVENTION
FIRST EMBODIMENT

25 FIG. 1 is a block diagram illustrating a general

21

configuration of a unit-to-unit data exchange system Sa with a
mediator server according to the first embodiment of the present
invention. Referring to FIG. 1, the unit-to-unit data exchange
system Sa with a mediator server includes a plurality of units
5 11, an exchange completion data keeping device 21, a public data
keeping device 31 and a channel 41. Note that it is assumed in
FIG. 1 that a unit 11a and a unit lib are exchanging data with
each other. Hereinafter, the designation "unit 11" will be used
where the exchanging unit is not particularly specified, and the

10 designation "unit 11a" or "unit lib" will be used where a particular
exchanging unit is specified. Note that the numbers of the units
11, the exchange completion data keeping devices 21, the public
data keeping devices 31 and the channels 41 are not limited to
those shown in FIG. 1.

15 The unit 11 is a computer device having a communications

function such as a personal computer, a portable communications
terminal or a mobile phone, and is owned by an exchanging party.
The unit 11 stores its data in a storage device such as a hard
disk or a memory. The unit 11 makes public a list of exchangeable

20 data from among all its stored data, by registering it at the public
data keeping device 31. The user operating the unit 11 refers
to the list of public data registered at the public data keeping
device 31 to identify another unit 11 that has data of interest.
If the user wishes to exchange data with the other unit 11, the

25 user's unit 11 communicates with the other unit 11 to exchange

22

data owned by the user 1 s unit 11 with data owned by the other unit
11. In a data exchange, the unit 11 converts data owned by the
unit 11 through a predetermined conversion method into data that
cannot be reproduced by itself, and transmits the converted data
5 to the other unit 11. When exchanging data with the other unit
11, the unit 11 produces data (hereinafter referred to as "exchange
completion data") that is necessary for the exchanged data to be
reproduced successfully after the completion of the data exchange,
and transmits the exchange completion data to the exchange

10 completion data keeping device 21, which keeps the exchange
completion data. When the data exchange with the other party's
unit 11 is completed successfully, the unit 11 receives exchange
completion data produced by the other party's unit 11 and sent
from the exchange completion data keeping device 2 1 , and reproduces

15 the data obtained through the exchange by using the received
exchange completion data.

The exchange completion data will now be described. The
exchange completion data is data that is necessary for successfully
reproducing the data obtained from the other unit 11 through the

20 data exchange. A typical example of the exchange completion data
is a decryption key. Where a decryption key is used as the exchange
completion data, the unit 11, exchanging data with the other unit
11, uses an encryption algorithm as the predetermined conversion
method, and encrypts its data before transmitting the data . After

25 the data exchange is completed successfully, the unit 11 receives

a decryption key produced by the other party's unit 11 and sent
from the exchange completion data keeping device 21, and decrypts
the exchanged data by using the received decryption key. Thus,
the obtained data can be reproduced successfully. Hereinafter,
5 the predetermined conversion method will be referred to as the
data conversion method.

Note that other examples of the exchange completion data
include data of a climax portion of a film, data of a refrain portion
of a musical tune, and data obtained by randomly or regularly

10 thinning out the original data. Thus, where a portion of the
original data is used as the exchange completion data, the unit
11, reproducing the exchanged data, combines the obtained exchange
completion data with the exchanged data to obtain data that can
be reproduced successfully. Where a portion of the original data,

15 being the data to be exchanged, is used as the exchange completion
data, the predetermined conversion method may be a method of
removing a portion of the original data.

The exchange completion data keeping device 21 is a computer
device such as a server, and is owned by an exchange mediator.

20 The exchange completion data keeping device 21 keeps exchange
completion data produced by various units 11. The exchange
completion data keeping device 21 transmits exchange completion
data that it keeps to both of the two units 11 exchanging data
with each other if the exchange completion data keeping device

25 21 is notified of successful completion of the data exchange between

24

the units 1 1 .

The public data keeping device 31 is a computer device such
as a server, and is owned by a public data keeper. The public
data keeping device 31 keeps a public data list, i.e., a list of
data that is registered by the users of the units 11 as being data
that is allowed by the users to be exchanged.

While the channel 41 is typicallya high-speed communications
network using optical fibers such as FTTH, it is not limited thereto
as long as it is a communications medium via which electronic data
can be transmitted/received, such as ADSL, the Internet, satellite
broadcasting, a wireless communications network, a premises LAN,
or a wireless LAN.

FIG. 2 is a block diagram illustrating a functional
configuration of the inside of the unit 11. Referring to FIG.
2, the unit 11 includes a data conversion section 111, a message
handling section 112, a storage device controlling section 113,
a data storage device 114, a user input/output section 115 and
a data transmission/reception section 116.

The data conversion section 111 uses a predetermined data
conversion method to convert data sent from the message handling
section 112 according to a specified request . The data conversion
section 111 may be implemented by hardware such as a dedicated
LSI or by a program that is run by a general-purpose CPU.

The message handling section 112 communicates with the data
conversion section 111, the storage device controlling section

113, the user input/output section 115 and the data
transmission/reception section 116, and handles messages
therefrom. The message handling section 112 may be implemented
by hardware such as a dedicated LSI or by a program that is run
5 by a general-purpose CPU.

The storage device controlling section 113 inputs /outputs
data to/from the data storage device 114. The storage device
controlling section 113 may be implemented by hardware such as
a dedicated LSI or by a device driver of the data storage device

10 114 that is run by a general-purpose CPU.

The data storage device 114 is a storage device such as a
hard disk or a memory for recording various data. The data storage
device 114 stores data that may be made public. Each piece of
data that may be made public is assigned a public data ID associated

15 with the data ID of the data. Moreover, the public data ID is
associated with information that describes the substantial
contents of the data (hereinafter referred to as "contents
information") .

FIG. 3 is a diagram illustrating an exemplary data structure
20 of data including data IDs and associated public data IDs.
Referring to FIG. 3, in section D401, for example, the data ID
"DATA_ID-1111" and the public data ID " PUBLIC_DATA_ID- 1 1 1 1 " are
associated with each other. In section D402, the data ID
"DATA_ID-2222" and the public data ID "PUBLIC_DATA_ID-222 2 " are
25 recorded as being associated with each other.

FIG. 4 is a diagram illustrating an exemplary data structure
of data associated with the data IDs of FIG. 3. Referring to FIG.
4, section D501, for example, represents the data ID and section
D502 represents the substance of the data that is associated with
5 the data ID in section D501. The substance of data refers to,
for example, digital data of a film, a musical tune, etc. Thus,
the substance of data associated with each data ID is stored in
the data storage device 114.

FIG. 5 is a diagram illustrating a data structure of public

10 contents information associated with the public data IDs of FIG.
3. Section D601 represents the public data ID, and section D602
represents the public contents information that is associated with
the public data IDinsectionD601. The public contents information
includes, for example, the contents title and information

15 indicating how much right to the contents is remaining (the
remaining number of times the contents can be reproduced, and the
expiration date thereof) . Note that FIG. 5 shows an example where
the public contents information indicates "Contents title: The
Blue City", "Remaining number of times of reproduction: 7" and

20 "Expiration date: March 31, 2003".

The unit 11 uploads a list of public data IDs and associated
public contents information to the public data keeping device 31.
The list is kept by the public data keeping device 31 as a public
data list.

25 The user input/output section 115 includes an input device,

27

such as a keyboard, a mouse, a button switch, etc., for receiving
data inputs from the user operating the unit 11, a display device,
such as a CRT, an LCD, etc., for displaying the contents of data,
and a sound output device, such as a speaker, etc., for outputting
5 the contents of data as sound. The user input/output section 115
is responsible for a data input operation and a data output
operation .

The data transmission/reception section 116 is a
communications device, such as data circuit- terminating equipment,

10 etc., for transmitting/receiving data to/from the other unit 11,
the exchange completion data keeping device 21 and the public data
keeping device 31 via the channel 41.

FIG. 6 is a block diagram illustrating a detailed functional
configuration of the inside of the data conversion section 111.

15 Referring to FIG. 6, the data conversion section 111 includes an
unconverted data converting section 1111, an exchange completion
data production section 1112, a converted data converting section
1113 and a request determination section 1114.

The unconverted data converting section 1111 converts data

20 of the unit 11 based on a predetermined data conversion method.
The data before being converted will hereinafter be referred to
as unconverted data. The data^ after being converted^ will be
referred to as converted data. The unconverted data converting
section 1111 sends, to the message handling section 112, the

25 exchange completion data sent from the exchange completion data

production section 1112 and the converted data.

For example, where an encryption method is used as the
predetermined data conversion method, the unconverted data is
unencrypted data and the converted data is encrypted data. Where
a conversion method of removing a climax portion of a film is used
as the predetermined data conversion method, the converted data
is the data obtained by removing the climax portion . This similarly
applies to a conversion method in which a refrain portion is taken
out. Note that as the contents provider previously specifies the
climax portion or the refrain portion, the unconverted data
converting section 1111 can identify the portion. Where a method
of thinning out data is used as the predetermined data conversion
method, the unconverted data converting section 1111 produces the
converted data by removing specified portions to be thinned out
from the unconverted data.

The exchange completion data production section 1112
produces conversion process data that is necessary for the
conversion from the unconverted data to the converted data, and
exchange completion data that is necessary for restoring the
unconverted data from the converted data, and sends these data
to the unconverted data converting section 1111. Where an
encryption method is used as the data conversion method at the
unconverted data converting section 1111, the conversion process
data is an encryption key for encrypting data. Then, the exchange
completion data is decryption key data for decrypting the encrypted

data .

Where another method of removing a portion of data is used
as the data conversion method, the conversion process data is data
that specifies the portion to be taken out. Then, the exchange
5 completion data is the taken-out portion of the data. Note that
where a method of removing a portion of data is used as the data
conversion method, the flow of the process performed between the
exchange completion data production section 1112 and the
unconverted data converting section 1111 is reversed from that

10 shown in FIG. 6. In the following description, it is assumed for
the sake of simplicity that an encryption method is used as the
data conversion method unless otherwise specified. Even if other
data conversion methods are used, the feature that the exchange
completion data is produced and that the converted data can be

15 reproduced successfully only by using the exchange completion data
will not change substantially, and minor changes to the process
flow can be made easily.

The converted data converting section 1113 converts the
converted data obtained from the other unit 11 to unconverted data

20 by using the exchange completion data obtained from the exchange
completion data keeping device 21, and sends the unconverted data
to the message handling section 112. Specifically, where the
exchange completion data is a decryption key, the converted data
converting section 1113 decrypts the converted data, which has

25 been encrypted, by using the exchange completion data to obtain

the unconverted data.

The request determination section 1114 determines the
contents of the request sent from the message handling section
112 to perform a predetermined process. If the received request
5 is a request to convert unconverted data to converted data, the
request determination section 1114 sends the unconverted data,
which has been received together with the request, to the exchange
completion data production section 1112 . If the received request
is a request to convert converted data to unconverted data, the

10 request determination section 1114 sends the converted data and
the exchange completion data, which have been received together
with the request, to the converted data converting section 1113.

FIG. 7 is a block diagram illustrating a functional
configuration of the inside of the exchange completion data keeping

15 device 21. Referring to FIG. 7, the exchange completion data
keeping device 21 includes an exchange completion data transmission
determination section 211, a message handling section 212, a
storage device controlling section 213, a data storage device 214
and a data transmission/reception section 215.

20 The exchange completion data transmission determination

section 211 produces a determination table including unit IDs and
associated exchange completion data sent from the units 11, and
registers, in the determination table, information indicating
whether or not there has been a notification from the unit 11 that

25 the data exchange has been completed successfully. Based on the

registered information, the exchange completion data transmission
determination section 211 determines whether or not to transmit
the exchange completion data to the unit 11. Specifically, the
exchange completion data transmission determination section 211
5 determines that exchange completion data can be transmitted to
the units 11a and lib only when it receives a notification that
the data exchange has been completed successfully both from the
unit 11a and from the unit lib. The exchange completion data
transmission determination section 211 may be implemented by

10 hardware such as a dedicated LSI or by a program that is run by
a general-purpose CPU.

The message handling section 212 communicates with the
exchange completion data transmission determination section 211,
the storage device controlling section 213 and the data

15 transmission/reception section 215, and handles messages
therefrom. The message handling section 212 may be implemented
by hardware such as a dedicated LSI or by a program that is run
by a general-purpose CPU.

The storage device controlling section 213 inputs/outputs

20 data to/from the data storage device 214. The storage device
controlling section 213 may be implemented by hardware such as
a dedicated LSI or by a device driver of the data storage device
214 that is run by a general-purpose CPU.

The data storage device 214 is a storage device such as a

25 hard disk or a memory for recording various data . The data storage

device 214 stores exchange completion data sent from the unit 11,
together with the determination table used for determining whether
or not to transmit the exchange completion data . The determination
table includes the ID (hereinafter referred to as the "unit ID")
5 of the unit 11 that has transmitted the exchange completion data
and that is associated with the ID (hereinafter referred to as
the "exchange completion data ID" ) of the exchange completion data,
and a completion notification flag indicating whether or not there
has been a notification from the unit 11 associated with the unit

10 ID that the data exchange has been completed successfully.

FIG. 8 is a diagram illustrating an exemplary data structure
of the determination table . Referring to FIG . 8, in a determination
table D901 whose determination table ID is " JUDGE_TABLE_ID-1111",
for example, section D902 includes the unit ID "CLIENT_ID-1111",

15 the exchange completion data ID "END_DATA_ID- 1111" and the
completion notification flag "OFF" being associated with one
another, and section D903 includes the unit ID "CLIENT_ID-2222 " ,
the exchange completion data ID "END_DATA_ID-2222 " and the
completion notification flag "OFF" being associated with one

20 another. The completion notification flag is turned "ON" if there
is a notification that the reception of data being exchanged has
been completed successfully from the other party's unit, and is
turned "OFF" if there is a notification that the reception of data
being exchanged cannot be completed due to a certain abnormality

25 occurring during the data exchange . Thus, the determination table

is used to keep exchange completion data so that it is possible
to specify the unit from which the exchange completion data has
been transmitted.

FIG. 9 is a diagram illustrating an exemplary data structure
5 of exchange completion data associated with exchange completion
data IDs of FIG. 8. Referring to FIG. 9, section D1001 represents
the exchange completion data ID, and section D1002 represents the
substance of the exchange completion data associated with the
exchange completion data ID in section D1001. The substance of

10 exchange completion data herein refers to the contents of the
exchange completion data sent from the unit 11. Thus, the data
storage device 214 stores the exchange completion data together
with the determination table.

The data transmission/reception section 215 is a

15 communications device for transmitting/ receiving data to/from the
unit 11 and the public data keeping device 31 via the channel 41.

FIG. lOisablock diagram illustrating a detailed functional
configuration of the inside of the exchange completion data
transmission determination section 211. Referring to FIG. 10,

20 the exchange completion data transmission determination section
211 includes a determination table referencing section 2111, a
determination table production section 2112 and a request
determination section 2113.

The request determination section 2113 determines the

25 contents of the request sent from the message handling section

212 to perform a predetermined process. If the received request
is a request to register exchange completion data, the request
determination section 2113 sends the unit IDs of the receiving
unit and the offering unit and the exchange completion data IDs
5 from both of the units to the determination table production section

2112, and requests the determination table production section 2112
to produce a determination table. If the received request is a
request to determine whether or not to transmit the exchange
completion data based on a notification of data exchange completion

10 from the unit 11, the request determination section 2113 sends,
to the determination table referencing section 2111, the unit ID
of the unit 11 that has given the completion notification, the
determination table ID associated with the unit ID, and the
completion notification information included in the completion

15 notification, and requests the determination table referencing
section 2111 to determine whether or not to transmit the exchange
completion data.

Based on the data from the request determination section

2113, the determination table production section 2112 produces
20 and stores a determination table in the data storage device 214,

and sends the ID of the determination table to the message handling
section 212. Note that the path_^ via which the determination table
production section 2112 stores the determination table in the data
storage device 214_^_ is not shown in the figure.
25 Based on the data from the request determination section

2113, the determination table referencing section 2111 references
the determination table stored in the data storage device 214 to
determine whether or not to transmit the exchange completion data.
Specifically, only if the completion notification flags in the
5 determination table are both "OK", i.e., only if a notification
of the successful completion of the data exchange has been received
from both of the two units 11 exchanging data, the determination
table referencing section 2111 determines that the exchange
completion data can be transmitted. If it is determined that the
10 exchange completion data can be transmitted, the determination
table referencing section 2111 sends the unit ID of each receiving
unit 11 and the exchange completion data ID to the message handling
section 212.

FIG. 11 is a block diagram illustrating a functional
15 configuration of the inside of the public data keeping device 31.
Referring to FIG. 11, the public data keeping device 31 includes
a message handling section 311, a storage device controlling
section 312, a data storage device 313 and a data
transmission/reception section 314 .
20 The message handling section 311 communicates with the

storage device controlling section 312 and the data
transmission/reception section 314, and handles messages
therefrom. The message handling section 311 may be implemented
by hardware such as a dedicated LSI or by a program that is run
25 by a general-purpose CPU.

The storage device controlling section 312 inputs /outputs
data to/from the data storage device 313. The storage device
controlling section 312 may be implemented by hardware such as
a dedicated LSI or by a device driver of the data storage device
5 313 that is run by a general-purpose CPU.

The data transmission/reception section 314 is a
communications device for transmitting/ receiving data to/from the
unit 11 and the exchange completion data keeping device 21 via
the channel 41.

10 The data storage device 313 is a storage device such as a

hard disk or a memory for recording various data . The data storage
device 313 stores a public data list . The public data list includes
public data IDs and unit IDs of the units 11 registering the public
data (hereinafter referred to as the "registering unit IDs " ) . Each

15 public data ID is associated with contents information.

FIG. 12 is a diagram illustrating an exemplary data structure
of public data list. Referring to FIG. 12, for example, section
D1201 includes the registering unit ID "CLIENT_ID-1111" and the
public data ID " PUBLIC_DATA_ID- 1 1 1 1 " associated with each other,

2 0 and section Dl 2 02 includes the regis tering unit ID "CLIENT_ID-2 2 22 "
and the public data ID "PUBLIC_DATA_ID-2222 " associated with each
other .

FIG. 13 is a diagram illustrating an exemplary data structure
of contents information associated with public data IDs of FIG.
25 12. Referring to FIG. 13, section D1301 represents the public

data ID. Section D1302 represents the contents information
associated with the public data ID in section D1301. Note that
the contents information in FIG. 13 indicates "contents title:
The Blue City", "Remaining number of times of reproduction: 7"
5 and "Expiration date: March 31, 2003".

Now, the flow of the process in the unit-to-unit data exchange
system Sa having such a configuration as described above will be
described. The process in the present system can be divided into
three stages. The first stage is where the unit 11 registers its

10 public data at the public data keeping device 31 . The second stage
is where the unit 11a obtains, from the public data keeping device
31, a unit ID that is associated with the public data ID specified
by the user. The third stage is where the unit 11a exchanges data
with the unit lib through the mediation of the exchange completion

15 data keeping device 21. Now, an operation of the unit 11, the
exchange completion data keeping device 21 and the public data
keeping device 31 will be described stage by stage.
SEQUENCE IN PUBLIC DATA REGISTERING STAGE

First, referring to FIG. 14 and FIG. 15, an operation of
20 the unit 11 and the public data keeping device 31 in the stage
where the unit 11 registers its public data at the public data
keeping device 31 will be described.

FIG. 14 is a sequence diagram illustrating an operation of
the unit 11 and the public data keeping device 31 when the unit
25 11 registers the contents information on its public data at the

public data keeping device 31. In FIG. 14, the point in time at
which each step is performed is denoted by an open rectangle while
data, or the like, that is being exchanged is specified above a
corresponding arrow extending between functional blocks so as to
5 make clear what is the subject of the operation in the unit 11
and what data or message is being exchanged between functional
blocks. A software functional block can be implemented by a
function that is programmed to go along the flow as illustrated
in the sequence diagram. A hardware functional block can be

10 implemented by designing the hardware so that it goes along the
flow as illustrated in the sequence diagram. This similarly
applies to the other sequence diagrams subsequent to FIG. 14.

First, in response to an input operation by the user, the
user input/output section 115 of the unit 11 obtains the data ID

15 of the data that the user is requesting to be registered, notifies
the message handling section 112 of the obtained data ID, and
requests the message handling section 112 to register the public
data (step S1401) .

Then, in response to the public data registration request,

20 the message handling section 112 obtains the data ID included in
the request, notifies the storage device controlling section 113
of the data ID, and requests the storage device controlling section
113 to obtain the public data from the data storage device 114
(step S1402) .

25 Then, in response to the public data obtaining request, the

storage device controlling section 113 obtains the data ID included
in the request, obtains the public data ID associated with the
data ID and the contents information of the public data from the
data storage device 114, and transmits the obtained public data
5 ID and the contents information to the message handling section
112 (step S1403) .

Then, receiving the public data ID and the contents
information, the message handling section 112 produces a
REGI STER_PUBLIC_DATA message including the public data ID, the

10 contents information and the unit ID of the unit 11, and transmits
the message to the data transmission/reception section 116 (step
S1404) . Receiving the REGI STER_PUBLIC_DATA message, the data
transmission/reception section 116 transmits the message to the
public data keeping device 31 (step S1405) .

15 Receiving the REGI STER_PUBLIC_DATA message from the unit

11, the public data keeping device 31 produces a public data list
based on the public data ID and the unit ID included in the message,
stores the associated contents information, and transmits, to the
unit 11, an ACK message indicating the result of the data

20 registration process (step S1406).

Receiving the ACK message from the public data keeping device
31, the data transmission/reception section 116 transmits the
message to the message handling section 112 (step S1407).

Receiving the ACK message, the message handling section 112

25 transmits the registration result information included in the

message to the user input/output section 115 (step S1408). In

response to this, the user input/output section 115 notifies the

user of the registration result information by displaying it on

the screen, etc. (step S1409).
5 FIG. 15 is a sequence diagram illustrating an operation of

the public data keeping device 31 and the unit 11 when the public

data keeping device 31 receives a REGI STER_PUBLIC_DATA message.

In FIG. 15, the same operations as those shown in FIG. 14 will

be denoted by the same step numbers and will not be further described
10 below. Note that the sequence diagram of FIG. 15 shows, in greater

detail, the operation of the public data keeping device 31 in step

S1406 of FIG. 14.

First, the data transmission/reception section 314 of the

public data keeping device 31 receives the REGI STER_PUBLIC_DATA
15 message from the unit 11, and transmits the message to the message

handling section 311 (step S1501).

Then, receiving the REGI STER_PUBLIC_DATA message, the

message handling section 311 extracts the public data ID, the

contents information and the unit ID from the message, and transmits
20 a public data registration request including the extracted

information to the storage device controlling section 312 (step

S1502) .

Receiving the public data registration request, the storage
device controlling section 312 produces a public data list in which
25 the public data ID and the contents information included in the

41

request are associated with each other and the public data ID and
the unit ID are associated with each other, stores the produced
list in the data storage device 313, and transmits the registration
result to the message handling section 311 (step S1503) .
5 Receiving the registration result, the message handling

section 311 transmits an ACK message including the registration
result information to the data transmission/reception section 314
(step S1504). Receiving the ACK message, the data

transmission/reception section 314 transmits the message to the
10 unit 11 (step S1505) .

SEQUENCE IN UNIT ID OBTAINING STAGE

Now, referring to FIG. 16 and FIG. 17, an operation of the
unit 11a and the public data keeping device 31 in the stage where
the unit 11a obtains, from the public data keeping device 31, a

15 unit ID that is associated with the public data ID specified by
the user will be described.

FIG. 16 is a sequence diagram illustrating an operation of
the unit 11a when obtaining the unit ID. First, the user
input/output section 115 of the unit 11a obtains the public data

20 ID of the requested data specified by an input from the user, and
transmits a request to obtain a registering unit ID, including
the public data ID, to the message handling section 1 12 (stepS1601) .
It is assumed herein that the public data ID can be obtained from
the public data list, etc. , made public at the public data keeping

25 device 31 . It is assumed herein that the unit 11a obtains a public

42

data ID registered by the unit lib.

Then, receiving the request to obtain a registering unit
ID, the message handling section 112 obtains the public data ID
included in the request, produces an OBTAIN_REGISTERING_UNIT_ID
5 message including the obtained public data ID, and transmits the
produced message to the data transmission/reception section 116
(step S1602) .

Receiving the OBTAIN_REGISTERING_UNIT_ID message, the data
transmission/reception section 116 transmits the message to the

10 public data keeping device 31 (step S1603).

Receiving the OBTAIN_REGISTERING_UNIT_ID message from the
unit 11a, the public data keeping device 31 obtains a registering
unit ID that is associated with the public data ID included in
the message (the unit ID of the unit 1 lb in the illustrated example) ,

15 and transmits an ACK message including the registering unit ID
to the unit 11a (step S1604) .

Receiving the ACK message from the public data keeping device
31, the data transmission/reception section 116 transmits the
message to the message handling section 112 (step S1605).

20 Receiving the ACK message, the message handling section 112
extracts the registering unit ID from the message, and transmits
the registering unit ID to the user input/output section 115 (step
S1606). The user input/output section 115 uses the received
registering unit ID for identifying the unit with which to exchange

25 data.

FIG. 17 is a sequence diagram illustrating an operation of
the public data keeping device 31 and the unit 11a when the public
data keeping device 31 receives an OBTAIN_REGISTERING_UNIT_ID
message. In FIG. 17, the same operations as those shown in FIG.
5 16 will be denoted by the same step numbers and will not be further
described below. Note that the sequence diagram of FIG. 17 shows,
in greater detail, the operation of the public data keeping device
31 in step S1604 of FIG. 16.

First, the data transmission/reception section 314 of the
10 public data keeping device 31 receives an

OBTAIN_REGISTERING_UNIT_ID message from the unit 11a, and
transmits the message to the message handling section 311 (step
S1701) .

Receiving the OBTAIN_REGISTERING_UNIT_ID message, the
15 message handling section 311 extracts the public data ID from the
message, and transmits a request to obtain a registering unit ID,
including the extracted ID, to the storage device controlling
section 312 (step S1702) .

Receiving the request to obtain a registering unit ID, the
20 storage device controlling section 312 obtains a registering unit
ID that is associated with the public data ID included in the request
from the data storage device 313, and transmits the registering
unit ID to the message handling section 311 (step S1703) .

Receiving the registering unit ID, the message handling
25 section 311 produces an ACK message including the registering unit

44

ID, and transmits the ACK message to the data
transmission/reception section 314 (step S1704).

Receiving the ACK message, the data transmission/reception
section 314 transmits the message to the unit 11a (step S1705) .
5 SEQUENCE IN DATA EXCHANGE STAGE

Now, referring to FIG. 18 to FIG. 26, the sequence in the
stage where the two units 11a and lib exchange data therebetween
through the mediation of the exchange completion data keeping
device 21 will be described.

10 FIG. 18 is a sequence diagram illustrating an operation of

the unit 11a and the unit lib from when the unit 11a requests the
unit lib to exchange data until the unit 11a receives a response
thereto. First, the user input/output section 115 of the unit
11a obtains the public data ID of the data requested by the user

15 and the unit ID of the unit to which the requested data belongs
(the unit ID of the unit that has registered the public data ID
at the public data keeping device 31) , and transmits a data exchange
request including the two IDs to the message handling section 112
(step S1801) . The process of obtaining the public data ID and

20 the unit ID has been described above with reference to FIG. 16
and FIG. 17.

Receiving the data exchange request, the message handling
section 112 transmits, to the storage device controlling section
113, a public data obtaining request to obtain the public data
25 IDs of all the data that the unit 11a has registered at the public

data keeping device 31 and all the contents information associated
with the public data IDs from the data storage device 114 (step
S1802) .

Then, receiving the public data obtaining request, the
5 storage device controlling section 113 obtains the public data
IDs of all the data that the unit 11a has registered at the public
data keeping device 31 and the associated contents information
from the data storage device 114, and transmits the obtained
information to the message handling section 112 (step S1803) .

10 Then, the message handling section 112 receives the public

data IDs and the contents information, and transmits, to the data
transmission/reception section 116, an EXCHANGE_DATA message
including the received information together with the unit ID and
the public data ID obtained in step S1801 (step S1804) .

15 Inresponseto this , the data transmission/ reception section

116 transmits the received EXCHANGE_DATA message to the unit lib
(step S1805) .

Receiving the EXCHANGE_DATA message from the unit 11a, the
unit lib selects the public data ID of the data requested by the

20 user from the message, and transmits an ACK message including the
selected public data ID to the unit 11a, according to the operation
shown in FIG. 23 to be described below (step S1806) . Note however
that if the unit lib does not have the data requested by the user,
the unit lib transmits an ACK message indicating the absence of

25 the requested data.

Receiving the ACK message from the unit lib, the data
transmission/reception section 116 transmits the message to the
message handling section 112 (step S1807).

FIG. 19 is a sequence diagram illustrating an operation of
5 the unit 11a and the exchange completion data keeping device 21
from when the unit 11a requests the exchange completion data keeping
device 21 for mediation until the unit 11a receives a response
thereto in a case where an ACK message received from the unit lib
includes a public data ID of data requested by the unit 11a. In
10 FIG. 19, the same operations as those shown in FIG. 18 will be
denoted by the same step numbers and will not be further described
below .

The message handling section 112 receives an ACK message,
and determines whether or not the exchanged data ID is included

15 in the ACK message . If it is included, the message handling section
112 transmits an exchanged data obtaining request including the
exchanged data ID to the storage device controlling section 113
(step S1808) . If it is not included, the message handling section
112 transmits information indicating the absence thereof to the

20 user input/output section 115. In response to this, the user
input/output section 115 notifies the user that the data exchange
has been refused by the unit lib.

Next, receiving the exchanged data obtaining request, the
storage device controlling section 113 references the data storage

25 device 114 to obtain the data ID associated with the exchanged

data ID included in the request and obtain data that is associated
with the data ID, and transmits the obtained data (hereinafter
referred to as the "exchanged data" ) to the message handling section
112 (step S1809) .
5 Receiving the exchanged data, the message handling section

112 transmits the exchanged data to the data conversion section
111, and issues a request to convert the exchanged data to obtain
converted data (hereinafter referred to as the "data conversion
request") (step S1810) .

10 Receiving the data conversion request, the data conversion

section 111 converts the unconverted data included in the request
to produce the converted data and the exchange completion data,
and transmits the converted data and the exchange completion data
to the message handling section 112 (step S1811).

15 Then, receiving the converted data and the exchange

completion data, the message handling section 112 produces a
REG I S TER_EXCHANGE_COMPLE T I ON_DAT A me s s age including the exchange
completion data and the unit ID, and transmits the produced message
to the data transmission/reception section 116 (step S1812).

20 Receiving the REGI STER_EXCHANGE_COMPLET ION_DATA message,

the data transmission/reception section 116 transmits the message
to the exchange completion data keeping device 21 (step S1813) .

Note that although the operation of the unit lib will not
be described herein, the unit lib performs a similar operation

25 to that of the unit 11a to transmit exchange completion data to

the exchange completion data keeping device 21.

Receiving the REGI STER_EXCHANGE_COMPLETION_DATA message
from the unit 11a and from the unit lib, the exchange completion
data keeping device 21 produces a determination table and stores
5 therein the exchange completion data included in the received
message, and then transmits an ACK message including the
determination table ID to the unit 11a and the unit lib, according
to the operation shown in FIG. 24 to be described below (step SI 8 14) .

Then, receiving the ACK message from the exchange completion
10 data keeping device 21, the data transmission/reception section
116 of the unit 11a transmits the message to the message handling
section 112 (step S1815) .

FIG. 20 is a sequence diagram illustrating an operation of
the unit 11a and the unit lib from when the unit 11a receives an
15 ACK message from the exchange completion data keeping device 21
until the unit 11a starts a data exchange with the unit lib. In
FIG. 20, the same operations as those shown in FIG. 19 will be
denoted by the same step numbers and will not be further described
below .

20 First, receiving the ACK message, the message handling

section 112 of the unit 11a transmits an INITIATE_EXCHANGE message
to the data transmission/reception section 116 (step S1816).

Then, receiving the INITIATE_EXCHANGE message, the data
transmission/reception section 116 transmits the message to the

25 unit lib (step S1817) .

Receiving the INITIATE_EXCHANGE message from the unit 11a,
the unit lib produces an ACK message and transmits the message
to the unit 11a, according to the operation shown in FIG. 25 to
be described below (step S1818).
5 Receiving the ACK message from the unit lib, the data

transmission/reception section 116 of the unit 11a transmits the
message to the message handling section 112 (step S1819).

Then, the data exchange is initiated between the unit 11a
and the unit lib (step S1820) . The communications method used

10 for the data exchange may be a method well known in the art such
as a packet-based communications method.

FIG. 21 is a sequence diagram illustrating an operation of
the unit 11a and the exchange completion data keeping device 21
from when the unit 11a terminates the communication session with

15 the unit lib until the unit 11a receives an ACK message from the
exchange completion data keeping device 21. In FIG. 21, the same
operations as those shown in FIG. 20 will be denoted by the same
step numbers and will not be further described below.

First, when the communication session with the unit lib is

20 terminated, the message handling section 112 determines whether
or not the exchanged data of interest has been obtained successfully
from the unit lib (step S1821a) . The determination of whether
or not each unit has obtained data successfully can be made as
follows. The units 11a and lib may previously exchange sizes of

25 data to be transmitted to each other, and each unit can determine

that the exchanged data could not be received successfully if the
size of the received data is smaller than the scheduled data size.

If the data has been obtained successfully, the message
handling section 112 produces an EXCHANGE_COMPLETED message
5 including information that indicates the completion of the exchange
(hereinafter referred to as the "OK information") and the
determination table ID (step S1821b) . If the data has not been
obtained successfully, the message handling section 112 produces
an EXCHANGE_COMPLETED message including information that

10 indicates the failure of the exchange (hereinafter referred to
as the "NG information") and the determination table ID (step
S1821c) . Then, the message handling section 112 transmits the
produced EXCHANGE_COMPLETED message to the data
transmission/reception section 116 (step S1821d).

15 Receiving the EXCHANGE_COMPLETED message, the data

transmission/reception section 116 transmits the message to the
exchange completion data keeping device 21 (step S1822) . Note
that although the operation of the unit lib will not be described
herein, the unit lib performs a similar operation to that of the

20 unit 11a to transmit an EXCHANGE_COMPLETED message to the exchange
completion data keeping device 21.

Receiving the EXCHANGE_COMPLETED message from the unit 11a
and from the unit lib, the exchange completion data keeping device
21 determines whether or not to send exchange completion data needed

25 by the unit 11a and exchange completion data needed by the unit

lib to the unit 11a and the unit lib, respectively, based on the
determination table, according to the operation shown in FIG. 26
to be described below. If it is determined that the exchange
completion data is to be transmitted, the exchange completion data
5 keeping device 21 transmits an ACK message including the exchange
completion data to the unit 11a and the unit lib. Ifitis determined
that the exchange completion data is not to be transmitted, the
exchange completion data keeping device 2 1 transmits an ACK message
that does not include the exchange completion data to the unit

10 11a and the unit lib (step S1823) . The determination of whether
or not to transmit the exchange completion data will be described
below in detail with reference to FIG. 26.

The data transmission/reception section 116 transmits the
ACK message from the exchange completion data keeping device 21

15 to the message handling section 112 (step S1824a) .

FIG. 22 is a sequence diagram illustrating an operation of
the unit 11a after receiving the ACK message from the exchange
completion data keeping device 2 1 . In FIG. 22, the same operations
as those shown in FIG. 21 will be denoted by the same step numbers

20 and will not be further described below.

First, the message handling section 112 analyzes the ACK
message from the exchange completion data keeping device 21 to
determine whether or not exchange completion data is included
therein (step S1825a) . If it is not included, the message handling

25 section 112 transmits information indicating the absence thereof

to the user input/output section 115. Then, since the exchange
completion data could not be obtained, the message handling section
112 notifies the user that the exchanged data cannot be reproduced
(step S1825b) .

5 If it is included, the message handling section 112 extracts

the exchange completion data, and transmits a data conversion
request including the exchange completion data and the converted
data obtained from the unit lib to the data conversion section

111 (step S1825c) .

10 Receiving the data conversion request, the data conversion

section 111 produces unconverted data based on the exchange
completion data and the converted data included in the request,
and transmits the unconverted data to the message handling section

112 (step S1826) .

15 Then, receiving the unconverted data, the message handling

section 112 transmits a data registration request including the
unconverted data to the storage device controlling section 113
(step S1827). Receiving the data registration request, the
storage device controlling section 113 extracts data included in

20 the request, newly assigns a data ID to the extracted data, registers
the extracted data at the data storage device 114, and transmits
information indicating the registration result to the message
handling section 112 (step S1828).

Then, receiving the information indicating the registration

25 result, the message handling section 112 transmits information

indicating the completion of the exchange to the user input/output
section 115 (step S1829) . Finally, the user input/output section
115 notifies the user of the completion of the data exchange (step
S1830) .

5 FIG. 23 is a sequence diagram illustrating an operation of

the unit lib when the unit lib receives an EXCHANGE_DATA message
from the unit 11a. In FIG. 23, the same operations as those shown
in FIG. 18 will be denoted by the same step numbers and will not
be further described below. FIG. 23 shows, in greater detail,

10 the operation of the unit lib in step S1806 of FIG. 18.

Receiving the EXCHANGE_DATA message from the unit 11a, the
data transmission/reception section 116 of the unit lib transmits
the message to the message handling section 112 (step S1901).

Then, receiving the EXCHANGE_DATA message, the message

15 handling section 112 extracts all the public data IDs and the
associated contents information from the message, and transmits
a data selection request including the extracted information to
the user input/output section 115 (step S1902).

Receiving the data selection request, the user input/output

20 section 115 presents all the public data IDs and the associated
contents information in the request to the user, and allows the
user to select data of interest to the user. In response to this,
the user selects data of interest from among the presented public
data. If there is no particular data of interest to the user,

25 the user makes a selection indicating the absence of data of interest.

The user input/output section 115 transmits the public data ID
that is associated with the public data selected by the user to
the message handling section 112 (step S1903) . Note that if no
particular data of interest is selected, the user input/output
5 section 115 transmits information indicating the absence of data
of interest to the message handling section 112 in place of the
public data ID.

Receiving the public data ID or the information indicating
that no data has been selected, the message handling section 112

10 transmits an ACK message including such information to the data
transmission/reception section 116 (step S1904) . Receiving the
ACK mess age, the data transmission/ reception section 116 transmits
the message to the unit 11a (step S1905).

FIG. 24 is a sequence diagram illustrating an operation of

15 the exchange completion data keeping device 21 when the exchange
completion data keeping device 21 receives a
REGI STER_EXCHANGE_COMPLET ION_DATA message from the unit 11a and
from the unit lib. In FIG. 24, the same operations as those shown
in FIG. 19 will be denoted by the same step numbers and will not

20 be further described below. FIG. 24 shows, in greater detail,
the operation of the exchange completion data keeping device 21
in step S1814 of FIG. 19.

Receiving the REGI STER_EXCHANGE_COMPLETION_DATA message
from the unit 11a and from the unit lib, the data

25 transmission/ reception section 215 of the exchange completion data

55

keeping device 21 transmits the message to the message handling
section 212 (step S2001) .

Receiving the REGI STER_EXCHANGE_COMPLET ION_DATA message,
the message handling section 212 transmits, to the exchange
5 completion data transmission determination section 211, a request
to produce a determination table including the exchange completion
data ID and the unit ID included in the message (step S2002) .

Receiving the determination table production request, the
exchange completion data transmission determination section 211
10 produces a determination table in which the unit ID and the exchange
completion data ID included in the request are associated with
each other, and transmits the determination table ID of the
determination table to the message handling section 212 (step
S2003) .

15 Receiving the determination table ID, the message handling

section 212 extracts the exchange completion data and the exchange
completion data ID from the REGI STER_EXCHANGE_COMPLET ION_DATA
message received from the unit 11a and from the unit lib, and
transmits an exchange completion data registration request

20 including the extracted information to the storage device
controlling section 213 (step S2004).

Then, receiving the exchange completion data registration
request, the storage device controlling section 213 stores the
exchange completion data and the exchange completion data ID

25 included in the request in the data storage device 214 so that

they are associated with each other, and transmits information
indicating the registration result to the message handling section
212 (step S2005) .

Receiving the information indicating the registration
5 result, the message handling section 212 transmits an ACK message
including the determination table ID to the data
transmission/reception section 215 (step S2006) . Receiving the
ACK mess age, the data transmission/ reception section 215 transmits
the message to the unit 11a and the unit lib (step S2007) .

10 FIG. 25 is a sequence diagram illustrating an operation of

the unit lib when the unit lib receives an INI T I ATE_EXCHANGE message
from the unit 11a. In FIG. 25, the same operations as those shown
in FIG. 20 will be denoted by the same step numbers and will not
be further described below. FIG. 25 shows, in greater detail,

15 the operation of the unit lib in step S1818 of FIG. 20.

Receiving the INITIATE_EXCHANGE message from the unit 11a,
the data transmission/reception section 116 of the unit lib
transmits the message to the message handling section 112 (step

52101) . Receiving the INITIATE_EXCHANGE message, the message
20 handling section 112 checks what are being exchanged, and transmits

an ACK message to the data transmission /reception section 116 (step

52102) . Receiving the ACK message, the data
transmission/reception section 116 transmits the message to the
unit 11a (step S2103) .

25 FIG. 26 is a sequence diagram illustrating an operation of

the exchange completion data keeping device 21 when the exchange
completion data keeping device 21 receives an EXCHANGE_COMPLETED
message from the unit 11a and from the unit lib. In FIG. 26, the
same operations as those shown in FIG. 21 will be denoted by the
5 same step numbers and will not be further described below. FIG.
26 shows, in greater detail, the operation of the exchange
completion data keeping device 21 in step S1823 of FIG. 21.

Receiving the EXCHANGE_COMPLETED message from the unit 11a
and from the unit lib, the data transmission/reception section

10 215 of the exchange completion data keeping device 21 transmits
the message to the message handling section 212 (step S2201).

Receiving the EXCHANGE_COMPLETED message from the unit 11a
and from the unit lib, the message handling section 212 extracts,
from each of the messages , the determination table ID, the exchange

15 completion information (the OK information indicating completion
of the exchange or the NG information indicating failure of the
exchange) and the unit ID, registers the extracted information
in the determination table, and requests the exchange completion
data transmission determination section 211 to determine whether

20 or not to transmit the exchange completion data to the units 11a
and lib while specifying a determination table ID of the
determination table (step S2202).

Receiving the request to determine whether or not to transmit
the exchange completion data, the exchange completion data

25 transmission determination section 211 references the

determination table associated with the determination table ID
included in the request to determine whether or not the OK
information is registered in both of the completion notification
flags of the unit IDs of the unit 11a and the unit lib (step S2203a) .
5 If the OK information is registered for both units, the exchange
completion data transmission determination section 211 transmits
the unit IDs and the associated exchange completion data ID to
the message handling section 212 and requests the message handling
section 212 to transmit the exchange completion data associated

10 with the unit ID of the unit lib to the unit 11a and to transmit
the exchange completion data associated with the unit ID of the
unit 11a to the unit lib (step S2203b) . If the NG information
is registered for either unit in the determination table, the
exchange completion data transmission determination section 211

15 transmits, to the message handling section 212, information
indicating that the exchange completion data cannot be transmitted,
and the message handling section 212 in response transmits, to
the unit 11a and the unit lib, an ACK message that indicates that
the exchange completion data cannot be obtained (steps S2203c and

20 S2203d) .

Receiving the unit ID and the exchange completion data ID,
the message handling section 212 transmits the exchange completion
data ID to the storage device controlling section 213 and requests
the storage device controlling section 213 to obtain the associated
25 exchange completion data from the data storage device 214

(hereinafter referred to as the "exchange completion data obtaining
request") (step S2204) .

Receiving the exchange completion data obtaining request,
the storage device controlling section 213 obtains exchange
5 completion data that is associated with the exchange completion
data ID included in the request from the data storage device 214,
and transmits the obtained exchange completion data to the message
handling section 212 (step S2205) .

Receiving the exchange completion data, the message handling

10 section 212 transmits, to the data transmission/reception section
215, ACK messages each including the exchange completion data such
that the exchange completion data associated with the unit ID of
the unit lib is transmitted to the unit 11a and the exchange
completion data associated with the unit ID of the unit 11a is

15 transmitted to the unit lib (step S2206). Receiving the ACK
messages, the data transmission/reception section 215 transmits
one of the messages to the unit 11a and the other to the unit lib
as specified (step S2207).

Thus, in the first embodiment, the data to be exchanged

20 between units will not themselves be uploaded to the exchange
completion data keeping device, but only those — the data (the
exchange completion data) that arc is necessary for completing
the data exchange arc is uploaded to the exchange completion data
keeping device. This reduces the problem that the communications

25 cost and the load on the mediator server increase in proportion

to the amount of data exchanged between units. In addition, two
units exchanging data with each other can obtain the exchange
completion data only when both of the units have successfully
received data of interest. Therefore, in the case of an abnormal
5 termination of the communication session, e.g., in the case of
disconnection on the side of one unit whereby the other unit fail
to successfully receive the data of interest, one of the units
that has terminated the communication session cannot obtain the
exchange completion data. Then, neither of the units will be able

10 to reproduce the data of interest. Thus, a fair data exchange
system is realized.

Moreover, the exchange completion data is produced by each
unit, thereby further reducing the load on the exchange completion
data keeping device. Each unit transmits its data to the other

15 party 1 s unit after converting it to data that cannot be reproduced
successfully without the use of exchange completion data.
Therefore, the other party's unit cannot successfully reproduce
the data unless it obtains the exchange completion data.

For example, a unit may encrypt data and transmit the

20 encrypted data to the other party's unit, and received data can
be reproduced by using a decryption key as encrypted exchange
completion data . Then, it is possible to easily realize the system
of the present invention by employing commonly-available
encryption/decryption software .

25 The exchange completion data keeping device determines

whether or not each unit exchanging its data with another has
successfully received data based on the communication result sent
from the unit. Therefore, it is possible to easily determine
whether or not the data exchange has been performed successfully.
5 The program of the present invention can be distributed to

each party f s computer device to realize an easy-to-use unit-to-unit
data exchange system, thus facilitating the circulation of
information contents .

Note that the operation of each of the unit 11, the exchange

10 completion data keeping device 21 and the public data keeping device
31 illustrated in the first embodiment can be implemented by a
program to be run by a general-purpose computer device. Such a
program is stored in a storage medium such as a hard disk, an optical
disk, a CD-ROM, a memory, or the like, and is run by a CPU, or

15 the like.

Note that while each unit produces and transmits the exchange
completion data to the exchange completion data keeping device
in the first embodiment, the exchange completion data keeping
device may produce the exchange completion data. A system where

20 the exchange completion data keeping device produces the exchange
completion data will now be described. For example, where a
decryption key is used as the exchange completion data, each unit
wishing to exchange data with another unit requests the exchange
completion data keeping device to produce a decryption key. In

25 response to this, the exchange completion data keeping device

produces a decryption key and a corresponding encryption key. The
exchange completion data keeping device registers, in the
determination table, the requesting unit that has made the request
to produce the decryption key so that it can later be identified.
5 Then, the exchange completion data keeping device transmits the
produced encryption key to the requesting unit. Receiving the
encryption key, the unit encrypts the data to be exchanged using
the encryption key to produce the converted data. The converted
data can be decrypted by using the decryption key registered in

10 the exchange completion data. The unit transmits the converted
data, which has been encrypted, to the other party's unit, and
obtains data of interest from the other party f s unit . Thereafter,
as in the embodiment described above, the unit obtains the
decryption key from the exchange completion data keeping device

15 to recover and reproduce the converted data that it has received
from the other party's unit. Thus, where the exchange completion
data keeping device produces the decryption key, the exchange
completion data keeping device produces the encryption key
corresponding to the decryption key at the same time, and returns

20 the encryption key to the unit that has made the request to produce
the decryption key. The encryption key can be said to be data
used for converting the unconverted data (hereinafter referred
to as the "conversion process data") so that the converted data
can be reproduced successfully by using the decryption key. Also

25 in this case, the exchange completion data may alternatively be

something other than a decryption key. Moreover, the conversion
process data may alternatively be something other than an
encryption key. Furthermore, in the system where the exchange
completion data is produced by the exchange completion data keeping
5 device, the unit and the exchange completion data keeping device
may be each implemented by a program instructing a computer device
to perform operations as described above. Thus, if the exchange
completion data keeping device produces the exchange completion
data, the unit does not have to have means for producing the exchange

10 completion data, whereby it is possible to reduce the load on the
unit. This is advantageous where units with small processing
capacities are used.

In the first embodiment, the units previously exchange sizes
of data to be transmitted to each other, and each unit can determine

15 that the exchanged data could not be received successfully if the
size of the received data is smaller than the scheduled data size.
However, the method for determining whether or not the exchanged
data has been received successfully is not limited to this. For
example, each unit may calculate the hash value of the converted

20 data, and register the hash value at the exchange completion data
keeping device 21, together with the exchange completion data.
Then, each unit, after finishing the communication session with
the other unit, can calculate the hash value of the received data
and transmits the hash value to the exchange completion data keeping

25 device 21. In response to this, the exchange completion data

keeping device 21 compares the received hash value with the
registered hash value. The exchange completion data keeping
device 21 determines that the data exchange has been performed
successfully if the hash values match with each other, and that
5 the data exchange has not been performed successfully if the hash
values do not match with each other. The use of a hash value is
advantageous in that it can be determined that the data exchange
has been performed successfully even if a portion of the exchanged
data is lost along the channel, whereby the size of the received

10 data is less than the scheduled size but the obtained exchanged
data can still be reproduced. It is understood that the present
invention is not limited to what has been described above, as long
as each unit sends the communication result with which the exchange
completion data keeping section can determine whether or not the

15 data exchange has been performed successfully.

In the first embodiment, each unit transmits the NG
information to the exchange completion data keeping device if the
exchanged data has not been received successfully. However, it
is not necessary to transmit the NG information if the exchange

20 completion data keeping section transmits the exchange completion
data only when the OK information is received from both of the
two units.

The process of deleting the exchange completion data stored
in the exchange completion data keeping device 21 will now be
25 described. FIG. 27 is a flow chart illustrating an operation of

the exchange completion data keeping device 21 until exchange
completion data is deleted. The operation illustrated in FIG.
27 is performed after the exchange completion data keeping device
21 transmits the ACK message in FIG. 26.
5 First, the exchange completion data keeping device 21

references the determination table to determine whether or not
the OK information has been transmitted from both of the two units
11a and lib exchanging data with each other (step S2701) . If the
OK information has been transmitted from both of the units, the

10 exchange completion data keeping device 21 determines whether or
not the ACK message, indicating that the exchange completion data
has been obtained successfully, has been received from both of
the units 11a and lib (step S2702) .

If so, indicating that the exchange completion data has been

15 received successfully by both of the units 11a and lib, the exchange
completion data keeping device 21 deletes the stored exchange
completion data and the associated determination table (stepS2703) ,
and exits the process. If not, indicating that the exchange
completion data has not successfully reached the unit or units

20 due to a communications abnormality, etc. , the exchange completion
data keeping device 21 resends the exchange completion data to
the unit that has transmitted the ACK message indicating the failure
to successfully obtain the exchange completion data (step S2704) ,
and the process returns to step S2702.

25 If the OK information has not been received from both of

the units in step S2701, the exchange completion data keeping device
21 determines whether or not the NG information has been received
from either unit (step S2705) . If the NG information has been
received from either unit, the exchange completion data keeping
5 device deletes the stored exchange completion data and the
associated determination table (step S2703) , and exits the process .

In a case where the NG information has not been received
from either unit and there has been no response from either one
of the units, the exchange completion data keeping device 21

10 determines whether or not a predetermined amount of time has elapsed
(step S2706) . If not, the exchange completion data keeping device
21 returns to step S2701. If it has elapsed, the exchange
completion data keeping device 21 deletes the stored exchange
completion data and the associated determination table (stepS2703) ,

15 and exits the process.

Thus, if a predetermined condition is met, the exchange
completion data is deleted from the network, whereby it is possible
to prevent the exchange completion data from being left unremoved
for a long time and being misused.

20 SECOND EMBODIMENT

The second embodiment of the present invention is directed
to a system where even if one unit fails to fully receive the
exchanged data from the other unit after receiving a portion thereof,
the unit can obtain the remaining portion of the exchanged data.

25 In the second embodiment, the overall system configuration is

similar to that of the first embodiment, and thus FIG. 1 will be
referred to in the following description of the second embodiment.

FIG. 28 is a sequence diagram illustrating an operation of
the unit 11a and the unit lib when the unit 11a requests the unit
5 lib to resend data to be exchanged. First, when finishing the
communication session with the unit lib, the message handling
section 112 of the unit 11a determines whether or not the size
of the received data is smaller than the total data size previously
sent from the unit lib (step S2801) .

10 If so, the message handling section 112 instructs the data

transmission/reception section 116 to send a resend request,
including the size of the already received data, to the unit lib
(step S2802) . In response to this, the message handling section
112 of the unit lib identifies the remaining data based on the

15 size of the already received data, instructs the storage device
controlling section 113 to obtain the remaining data from the data
storage device 114, and instructs the data transmission/reception
section 116 to transmit the remaining data to the unit 11a (step
S2803) . The unit 11a receives the remaining data transmitted from

20 the unit lib, combines the remaining data with the already received
data, stores the combined data, and returns to step S2801.

If not, i.e., if the size of the received data is the same
as the scheduled total size, the message handling section 112
instructs the data transmission/reception section 116 to transmit

25 an EXCHANGE_COMPLETED message, which indicates successful data

reception, to the exchange completion data keeping device 21 (step
S2805) , receives the exchange completion data from the exchange
completion data keeping device 21 (step S2806), and exits the
process. Note that if the unit lib gives a resend request to the
5 unit 11a, the unit lib may operate as described above.

Thus, if a unit fails to fully receive data of interest,
the unit gives a resend request to the other party 1 s unit, whereby
the unit can fully receive the data of interest.

In the above description, it is assumed that the unit lib

10 transmits the remaining data in response to a resend request.
However, if the unit lib is unable to be connected, the unit 11a
cannot successfully receive the remaining data, in which case an
exchange completion notification indicating the failure to
successfully receive the data is transmitted to the exchange

15 completion data keeping device 21.

In an embodiment where the exchange completion data is
produced by the exchange completion data keeping device 21, when
the unit lib resends the exchanged data in response to a resend
request from the unit 11a, the unit lib may again obtain the

20 conversion process data and the exchange completion data from the
exchange completion data keeping device 21 to produce the converted
data. In such a case, the unit lib can send the converted data
starting from the beginning thereof . Then, the unit 11a, receiving
the converted data starting from the beginning thereof, can discard

25 the already received data.

THIRD EMBODIMENT

The third embodiment of the present invention is directed
to a system in which the data exchange process is simplified
depending on the user with which data is being exchanged. In the
5 third embodiment, the overall system configuration is similar to
that of the first embodiment, and thus FIG. 1 will be referred
to in the following description of the third embodiment.

In the third embodiment, the unit 11 stores its history of
data exchanges made with other units in the data storage device

10 114. FIG. 2 9 is a diagram illustrating an exemplary data structure
of an exchange history stored in the unit 11. Referring to FIG.
29, the exchange history includes the unit ID of the other party's
unit, the number of data exchanges that have been made with the
unit, the number of successful data exchanges that have been made

15 with the unit, the success percentage calculated based on the number
of data exchanges and the number of successful data exchanges,
the data reception rate from the last data exchange, and the storage
location of the received data from the last data exchange
(hereinafter referred to as the "last data storage location").

20 When exchanging data with the other unit 11, the unit 11 registers
the result of the data exchange as the exchange history at the
data storage device 114.

FIG. 30 is a flow chart illustrating an operation of the
unit 11a when requesting the unit lib to exchange data. First,

25 the message handling section 112 of the unit 11a produces an

EXCHANGE_DATA message addressed to the unit lib, and instructs
the data transmission/reception section 116 to transmit the
produced message (step S3001). Then, the unit 11a receives an
ACK mess age from the unit lib, and identifies the public data thereof
5 being selected (step S3002) .

Then, referring to the exchange history, the unit 11a
determines the method of producing the exchange completion data
(step S3003) . There are various methods of producing the exchange
completion data. For example, possible methods include: if the

10 number of exchanges is 5 or more and the success percentage is
95%, the unit 11a may transmit the requested data as it is to the
unit lib without subjecting it to a data conversion operation such
as an encryption operation; if the number of exchanges is 5 or
more and the success percentage is equal to or greater than 80%

15 and less than 95%, the requested data maybe encrypted with a 128-bit
encryption key, while a decryption key corresponding to the
encryption key is used as the exchange completion data; if the
number of exchanges is 5 or more and the success percentage is
less than 80%, the requested data may be encrypted with a 1024-bit

20 encryption key, while a decryption key corresponding to the
encryption key is used as the exchange completion data; and if
the number of exchanges is less than 5, the requested data may
be encrypted with a 512-bit encryption key, while a decryption
key corresponding to the encryption key is used as the exchange

25 completion data. Thus, by using a shorter encryption key for a

71

higher success percentage, the operation required for the
decryption process is reduced for a unit of a trusted party. For
example, in the example illustrated in FIG. 29, the requested data
will not be encrypted for the unit having the unit ID "C0001".
5 The requested data will be encrypted with a 512-bit encryption
key for the unit having the unit ID "C0002". The requested data
will be encrypted with a 1024-bit encryption key for the unit having
the unit ID "C0003". Note that the method for producing the
exchange completion data is not limited to those described above.

10 Then, the unit 11a produces the converted data and the

exchange completion data using the data production method selected
in step S3003 (step S3004), transmits the produced exchange
completion data to the exchange completion data keeping device
21 (step S3005) , initiates the data exchange process (step S3006) ,

15 and exits the process.

Thus, by producing the exchange completion data based on
the history of data exchanges made with other units, it is possible
to simplify the data recovery process at the other party's unit.
Thus, it is possible to provide an easy-to-use system in which

20 an exchange with a highly trusted party can be performed quickly.
Moreover, a unit may simplify the conversion of data to be
transmitted based on its history of data exchanges made with other
units, whereby a data exchange with a highly trusted party can
be performed more quickly.

25 The above embodiment is directed to an operation where the

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exchange completion data is produced within a unit. An operation
where the exchange completion data is produced by the exchange
completion data keeping device will now be described.

FIG. 31 is a flow chart illustrating an operation of the
5 unit 11a when producing exchange completion data at the exchange
completion data keeping device. First, the message handling
section 112 of the unit 11a produces an EXCHANGE_DATA message
addressed to the unit lib, and instructs the data
transmission/reception section 116 to transmit the produced

10 message (step S3101) . Then, the unit 11a receives an ACK message
from the unit lib, and identifies the public data thereof being
selected (step S3102).

Then, referring to the exchange history, the unit 11a
determines the method for an exchange process to be performed at

15 the exchange completion data keeping device 21 (step S3103) . The
method for an exchange process herein refers to the method used
when converting data at the unit 11a. For example, in a case where
a data encryption process is used as the conversion process, the
unit 11a referring to the exchange history determines the length

2 0 of the encryption key used in the encryption process . It is assumed
that the unit 11a uses a shorter encryption key for a unit having
a higher exchange success percentage.

Then, the unit 11a notifies the exchange completion data
keeping device 21 of information indicating the selected method

25 for the exchange process (step S3104). In response to the

notification, the exchange completion data keeping device 21
produces the conversion process data used in the specified method
for the conversion process (e.g., an encryption key), and further
produces the exchange completion data corresponding to the
5 conversion process data (e.g., a decryption key). Then, the
exchange completion data keeping device 21 stores the produced
exchange completion data, and transmits the exchange completion
data to the unit 11a.

In response to this, the unit 11a receives the conversion

10 process data (step S3105) , produces the converted data using the
conversion process data (step S3106), and initiates the data
exchange with the unit lib.

Note that the data reception rate and the last data storage
location registered in the exchange history as illustrated in FIG.

15 29 are used when the unit 11a makes a resend request to the unit
lib after failing to successfully receive the data. It is assumed
that the units previously exchange sizes of data to be transmitted
to each other at the start of the data exchange process. Based
on the data reception rate, the unit 11a notifies the unit lib

20 of the communication result indicating how much of the data has
been received successfully. In response to this, the unit lib
identifies the remaining portion, which has not been transmitted
successfully, and resends the remaining portion to the unit 11a.
The unit 11a stores the resent data so that the data portion stored

25 in last data storage location and the remaining data being resent

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will be properly joined together.

Note that the units may previously exchange hash values of
data to be transmitted to each other at the start of the data exchange
process. In such a case, a requesting unit can calculate the hash
5 value of the received data to determine whether or not the data
has been fully received. If the data has not been fully received,
the requesting unit transmits the hash value of the received data
portion to the other party's unit. In response to this, the other
party's unit resends the remaining data, which can be identified
10 based on the hash value . Thus , by using a hash value , it is possible
to determine whether or not data of interest has been received
even if the data size is changed along the channel.

INDUSTRIAL APPLICABILITY

15 A unit- to -unit data exchange system of the present invention,

and a unit, an exchange completion data keeping device and a program
for use in such a system, can prevent an unfair exchange from taking
place without increasing the communications cost or the load on
the server, and are useful in, forexample, a system where electronic

20 data such as information contents are exchanged.

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ABSTRACT

Aft — ob j cct — — fefee — present — invention — ±s — fee — provide — a — A

unit-to-unit data exchange system preventing in which an unfair
5 exchange is prevented without increasing the communications cost
or the a load on the a server. A unit (11a) exchanges data with
a unit (lib) . An exchange completion data keeping device (21)
keeps exchange completion data that is necessary for each unit
(11a and lib) to reproduce the obtained data after the data exchange

10 is completed. The exchange completion data keeping device
transmits the exchange completion data obtained from the unit ( 1 lb)
to the unit (11a) and transmits the exchange completion data
obtained from the unit (11a) to the unit (lib) only when both of
the unit (11a) and the unit (lib) have successfully received data

15 of interest.

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